2. What Are Hydraulic Machines?
Machine which convert hydraulic energy( energy possessed
by water) into mechanical energy (which is further
converted into electrical energy)---turbine
Machine which convert mechanical energy into hydraulic
energy---pump
3. Hydraulic Turbines
Hydraulic Turbines have a row of blades fitted to the rotating
shaft or a rotating plate. Flowing liquid, mostly water, when pass
through the Hydraulic Turbine it strikes the blades of the turbine
and makes the shaft rotate. While flowing through the Hydraulic
Turbine the velocity and pressure of the liquid reduce, these
result in the development of torque and rotation of the turbine
shaft.
Classification of Hydraulic Turbines:
Based on flow path
Based on pressure change
Based on head
Based on specific speed
Based on disposition of turbine main shaft
4. Based On Flow Path
Axial Flow Hydraulic Turbines: This category of Hydraulic
Turbines has the flow path of the liquid mainly parallel to the
axis of rotation. Kaplan Turbines has liquid flow mainly in axial
direction.
Radial Flow Hydraulic Turbines: Such Hydraulic Turbines has the
liquid flowing mainly in a plane perpendicular to the axis of
rotation.
Mixed Flow Hydraulic Turbines: For most of the Hydraulic
Turbines used there is a significant component of both axial and
radial flows. Such types of Hydraulic Turbines are called as Mixed
Flow Turbines. Francis Turbine is an example of mixed flow type,
in Francis Turbine water enters in radial direction and exits in
axial direction.
5. Based On Pressure Change
Impulse Turbine: The pressure of liquid does not change
while flowing through the rotor of the machine. In Impulse
Turbines pressure change occur only in the nozzles of the
machine.
Example of impulse turbine: Pelton Wheel.
Reaction Turbine: The pressure of liquid changes while it
flows through the rotor of the machine. The change in fluid
velocity and reduction in its pressure causes a reaction on
the turbine blades; this is where from the name Reaction
Turbine may have been derived.
Examples: Francis and Kaplan Turbines fall in the category of
Reaction Turbines.
6. Based On Head
High head turbine (Above 250 m) Pelton Turbine
Medium head turbine (60 – 250 m) Francis Turbine
Low head turbine (Below 60 m)Kaplan Turbine
7. Based On Specific Speed
Specific speed Ns = N √P / H5/4
Low specific speed (8.5 – 30) - Pelton Turbine
Medium specific speed (50 – 340) - Francis Turbine
High specific speed (255 – 860) - Kaplan Turbine
Based On Disposition Of Turbine Main
Shaft
Horizontal shaft
Vertical shaft
9. Parts Of A Hydroelectric Plant
Dam. Raises the water level of the river to create falling water. Also
controls the flow of water. The reservoir that is formed is, in effect,
stored energy.
Turbine. The force of falling water pushing against the turbine's blades
causes the turbine to spin. A water turbine is much like a windmill,
except the energy is provided by falling water instead of wind. The
turbine converts the kinetic energy of falling water into mechanical
energy.
Generator. Connected to the turbine by shafts and possibly gears so
when the turbine spins it causes the generator to spin also. Converts the
mechanical energy from the turbine into electric energy. Generators in
hydropower plants work just like the generators in other types of power
plants.
Transmission lines. Conduct electricity from the hydropower plant to
homes and business.
10. Pelton Turbine/ Wheels
Water strikes the vanes along tangent of the runner and the
energy available at the inlet of turbine is only kinetic
energy, there fore is is a tangential flow impulse turbine
In a Pelton Turbine or Pelton Wheel water jets impact on the
blades of the turbine making the wheel rotate, producing
torque and power.
11. Main Parts Of A Pelton Wheel
Nozzle: it control the amount of water striking the vanes
of the runner
Casing: it is used to prevent splashing of water and plays
no part in power generation
Runner with bucket: runner is a circular disc on the
periphery of which a number of evenly spaced bucket are
fixed
Breaking jet: to stop the runner in short time breaking jet
is used
13. Working Principle of Pelton Turbine
Water jets emerging strike the buckets at splitter and split into two.
Stream flow along the inner curve of the bucket and leave it in the
direction opposite to that of incoming jet.
The high pressure water can be obtained from any water body
situated at some height or streams of water flowing down the hills.
The change in momentum (direction as well as speed) of water
stream produces an impulse on the blades of the wheel of Pelton
Turbine. This impulse generates the torque and rotation in the shaft
of Pelton Turbine.
Horizontal shaft - Not more than 2 jets are used and
Vertical shaft - Larger no. of jets (up to 6) are used.
Iron/Steel casing to prevent splashing of water and to lead water to
the tail race.
14. Francis Turbine
1st hydraulic turbine with radial inflow
Water flow from outward to inward, k/a inward radial
flow turbine
Francis turbine is a reaction turbine as the energy
available at the inlet of the turbine is a combination of
kinetic and pressure energy.
Water pressure decreases as it passes through the turbine
imparting reaction on the turbine blades making the
turbine rotate
15. Main Parts Of A Francis Turbine
Casing: the runner is completely enclosed in an air-tight
spiral casing. The casing and runner are always full of water
Guide mechanism: it consists of stationary circular wheel
on which stationary guide vanes are fixed. The guide vanes
allow the water to strike the vanes of the runner without
shock at inlet
Runner: is a circular wheel on which a series of curved
radial guide vanes are fixed
Draft tube: it is used for discharging water from the outlet
of the runner to the tail race.
18. Working Principle Of Francis Turbine
Francis Turbines are generally installed with their axis vertical.
Water with high head (pressure) enters the turbine through the spiral
casing surrounding the guide vanes.
The water looses a part of its pressure in the volute (spiral casing) to
maintain its speed.
Then water passes through guide vanes where it is directed to strike the
blades on the runner at optimum angles. As the water flows through the
runner its pressure and angular momentum reduces.
This reduction imparts reaction on the runner and power is transferred
to the turbine shaft.
If the turbine is operating at the design conditions the water leaves the
runner in axial direction.
Water exits the turbine through the draft tube, which acts as a diffuser
and reduces the exit velocity of the flow to recover maximum energy
from the flowing water.
19. Kalpan Turbine
Kalpan turbine is an axial flow reaction turbine
The water flows through the runner of the turbine in an axial direction
and the energy at the inlet of the turbine is the sum of kinetic and
pressure energy.
In an axial flow reaction turbine the shaft is vertical.
Lower end of shaft is k/a hub or boss.
On the hub vanes are attached. If the vanes are adjustable then it is k/a
kalpan turbine, if vanes are not adjustable then is k/a propeller turbine
Best suited where large quantity of low head water is available.
Kaplan Turbine has propeller like blades but works just reverse. Instead
of displacing the water axially using shaft power and creating axial
thrust, the axial force of water acts on the blades of Kaplan Turbine and
generating shaft power.
20. Main Parts Of A Kalpan Turbine
Scroll casing
Guide vane mechanism
Hub with vanes
Draft tube
23. Working Principle Of Kalpan Turbine
The working head of water is low so large flow rates are allowed in
the Kaplan Turbine.
The water enters the turbine through the guide vanes which are
aligned such as to give the flow a suitable degree of swirl
determined according to the rotor of the turbine.
The flow from guide vanes pass through the curved passage which
forces the radial flow to axial direction with the initial swirl
imparted by the inlet guide vanes which is now in the form of free
vortex.
The axial flow of water with a component of swirl applies force on
the blades of the rotor and looses its momentum, both linear and
angular, producing torque and rotation (their product is power) in
the shaft.
The scheme for production of hydroelectricity by Kaplan Turbine is
same as that for Francis Turbine.
24. Draft Tube
It is a pipe of gradually increasing area which connects
the outlet of the runner with the tailrace.
One end of the draft tube is connected to the outlet of
the runner while the other end is submerged below the
level of water in the tailrace
It creates a negative head at the outlet of the runner
thereby increasing the net head on the turbine
It converts a large proportion of rejected kinetic energy
into useful pressure energy
25. Governing of Turbines
It is the operation by which the speed of the turbine is
kept constant under all conditions of the working load.
This is done automatically by a governor which regulate
the rate flow through the turbine according to the
changing load condition on the turbine
It is absolutely necessary if the turbine is coupled to an
electric generator which is required to run at constant
speed under all fluctuating load conditions
